The present invention relates to a rotary type storage apparatus and a control technique thereof, and more specifically, to a rotary type storage apparatus and a control method thereof effectively applied to a rotary type storage apparatus or the like, for transferring data on a plurality of information tracks between a high order apparatus and the storage apparatus.
In conventional well known magnetic disk storage apparatuses and optical disk apparatuses used as external storage apparatuses for computer systems, a pair of data read/write heads (for instance, magnetic heads and optical heads) are selected so as to perform a data transfer operation for each information track.
More recently, performance of central processing units (CPU) of high order apparatuses and channel apparatuses for controlling data transmission and reception with respect to external apparatuses has rapidly improved, especially data processing speed. In connection therewith, performance (in particular, data transferring speed) of the external storage apparatuses such as the magnetic disk storage apparatus and the optical disk apparatus needs to be similarly improved.
Accordingly, a method has been proposed in, for instance, a magnetic disk storage apparatus that a plurality of magnetic heads commonly driven by a single access mechanism are simultaneously driven to transfer data on a plurality of information tracks at the same time. Furthermore, there is FBA (Fixed Block Architecture) type magnetic disk storage apparatus in which the recording unit of the data on the information track is selected to be a fixed length. In such external storage apparatuses, high speed data transfer operations containing the substitution (replacement) process for defects made on the recording medium are required.
Under such circumstances, in such a sort of rotary type information storage apparatus, generally speaking, the following substitution processing method has been employed. That is, the substitution sector regions corresponding to several sectors are reserved at the rear ends of the respective information tracks. In case that there is a recording medium defect at a certain sector of a certain track, the substitution sector of this sector is allocated to the above-described sector region on the same information track. When the regions containing the failed (defect) sector are read out, useless rotation waiting time is required for accessing the substitution sector into which the content of this failed sector has been stored. Accordingly, there is such a problem that input/output response time is considerably increased.
As a consequence, another conventional substitution processing method has been proposed that no useless rotation waiting time is required to read out the regions containing the failed sector. For instance, as described in JP-A-62-6243169, within the subsequent information track in the same cylinder of the information track belonging to the failed sector, the sector positioned at the same position as the failed sector in a circumferential direction of the recording medium is allocated as the substitution sector, and also when the failed sector belongs to the final track, the sector present in the head track at the position subsequent to the position of the above described failed sector is substituted as the substitute sector.
In FIG. 1, there is shown one example of the FBA type magnetic disk storage apparatus to which the above-described substitution processing method has been applied.
FIG. 1 represents a track format, and formats of 4 tracks (t.sub.0, t.sub.1, t.sub.2, t.sub.3) are identical to each other. It should be noted that although FIG. 1 shows a 4-track arrangement for the sake of convenience, the track arrangement is not limited thereto, generally speaking. Each of the tracks starts from an index signal 202, and is subdivided into (N+1) pieces of sectors 203 (0, 1, 2, ---, N). A single block 204 (B.sub.00, B.sub.01, B.sub.02,---, B.sub.ON, B.sub.10, B.sub.11, ---, B.sub.3N) is allocated to each of the sectors, and then both the data transfer operation between the high order apparatus and the storage medium, and the data read/write operation on the magnetic disk are carried out in units of this block. Also, one magnetic head is employed with each of these tracks, and four blocks (for instance, B.sub.00, B.sub.10, B.sub.20, B.sub.30) on the same sectors along the circumferential direction may be simultaneously read and written. It should be noted that each of the blocks is constructed of an ID part 205 on which the physical address (for example, track number, sector number) of this block has been recorded, and also a data part 206 on which the actual user data are recorded.
In general, since the data on the same sectors of the plural tracks along the circumferential direction are parallel-transferred one by one, the theoretical block transfer sequence is set to B.sub.00, B.sub.10, B.sub.20, B.sub.30, B.sub.01, B.sub.11, ---, B.sub.2N, B.sub.3N. Furthermore, four blocks (for instance, B.sub.00, B.sub.10, B.sub.20, B.sub.30) of the tracks "t.sub.O " to "t.sub.3 " at the same sector position (e.g., sector "0") are simultaneously read out, and the read blocks are once read into the data buffer in the magnetic disk storage apparatus. Then, while 4 blocks (for example, B.sub.01, B.sub.11, B.sub.21, B.sub.31) at the next sector position (e.g., sector 1) are read out and read into another data buffer, the previous 4 blocks (B.sub.00, B.sub.10, B.sub.20, B.sub.30) stored in the above-described data buffer are transferred to the high order apparatus. The above-described block processing operation is subsequently repeated. The order of the blocks transferred to the high order apparatus is determined, as previously stated, in the order of the tracks B.sub.00, B.sub.10, B.sub.20, B.sub.30, B.sub.01, B.sub.11, ---.
In general, according to the above-described method, if the data transfer capability of the high order apparatus (namely, channel apparatus) is "n" times higher than that of a single magnetic disk when the track number is "n", it is possible to transfer data consisting of "n" sectors while the magnetic head is advanced by 1 sector. Then, the effective data transfer velocity of the magnetic disk storage apparatus becomes "n" times higher than the data transfer speed achieved when the data are transferred trackwise.
Subsequently, in the conventional storage apparatus shown in FIG. 1, consideration is given to the defect produced in the recording medium, since when, for example, the block B.sub.20 of the sector "0" at the track "t.sub.2 " becomes a failed sector, the data (2) to be written into this block B.sub.20 have been recorded on the block B.sub.30 at the same sector of the subsequent track "t.sub.3 ", the data (2) may be read out therefrom without any useless rotation waiting time. When the block B.sub.31 of the sector 1 in the final track "t.sub.3 " becomes a failed sector, as the data (6) to be written into this block B.sub.31 have been recorded on the block B.sub.02 of the next sector in the track "t.sub.0 ", this data (6) may be read out, while waiting for 1 sector rotation time.
On the other hand, there is an optical disk as an information storage medium having a large memory capacity at lower recording cost, suitable for recording/reproducing a large quantity of data such as image information and document information. Since the present reliability of the data writing operation for such an optical disk is not sufficient, it is therefore required to maintain the reliability of the recorded data by simultaneously performing the readout check by the DRAW (Direct Read After Write) operation when the data are written into the optical disk. However, to allocate the substitution sector corresponding to the sector which has been judged as the failed sector by this DRAW operation, at least one sector just after this failed sector needs to be used. In accordance with the conventional technique as described in the above JP-A--62-243169, the substitution sector must be allocated at the same sector of the next track with respect to the failed sector, whereby it may be understood that the substitution process effected by the DRAW operation cannot be realized. As a result, if the above-described DRAW operation is applied to the above-described conventional techniques, the data cannot be written at the same time, and thus the readout check by the DRAW operation must be performed while sequentially writing the data while waiting for the respective disk rotations in unit of 1 sector in the order of the track. Then, there is a problem that the data writing velocity is considerably lowered.
Very recently, in the magnetic disk storage apparatus and optical disk storage apparatus, a data plane servo system has been widely utilized as the positioning method of the read/write head. In the conventional magnetic disk storage apparatus, the track on at least a certain plane of the disk is used as the servo track, and in connection with the positioning operations of a pair of read/write heads to this servo track, other read/write heads are positioned to the track on other disk plane. In accordance with the above-described data plane servo system, the information (for instance, address information such as track numbers and sector number) required for the positioning operation has been previously written on the respective tracks, so that the positioning operations may be separately performed in unit of each head. As a consequence, there are advantages that the distance between the adjoining tracks may be made very short and the memory capacity may be increased. In the above-described data plane servo type magnetic disk storage apparatus or optical disk storage apparatus, if the head drive mechanism capable of separately driving a plurality of tracks is employed, a plurality of tracks may be accessed in a parallel mode without mutual relationships. In this case, since the operations of the respective heads are not in synchronism with each other, the above-described substitution processing method as disclosed in the above-described Japanese patent KOKAI disclosure for the failed sector cannot be employed. Also, there is another problem in the access time to the common substitution sector region (namely to which a specific track on the disk plane has been allocated) when the substitution sectors consisting of several sectors are completely used in accordance with such a conventional method that several sectors are employed at the rear end of each track.